This invention relates to redirecting a beam of charged particles.
For medical diagnosis or therapy, it is often desirable to be able to have a beam strike the patient from any one of a range of different directions. In the case of an X-ray beam, the beam source may be compact enough to be moved about a stationary patient to achieve any desired beam direction.
Other kinds of beams (proton beams, for example) are generated by sources (e.g., cyclotrons) that are too massive to be conveniently moved relative to the patient. One way to achieve different beam directions is to move the patient relative to the fixed beam; but moving the patient has disadvantages.
It has also been proposed to hold the patient stationary (e.g., lying down) and provide a movable gantry capable of receiving the beam from the fixed beam source and routing it to the patient along any one of a range of different directions.
In one proposed gantry, the available beam directions all lie in a plane that intersects the tissue to be treated and is perpendicular to the original beam direction from the fixed source. The gantry is U-shaped and swings around an axis defined by the original beam. The original beam is first magnetically redirected typically by 90.degree. to enter one leg of the U and is then bent around the U to the other leg, which lies in the plane of treatment. The beam finally exits that second leg along a path directed toward the tissue. The volume of clear space required to accommodate the swinging gantry is governed by the width and height of the U.
In another proposed gantry system, the beam would first be magnetically redirected 45.degree. and then, after scattering, would be redirected (in the same plane) through an angle of 135.degree. to a path aimed toward the tissue.